Optical data storage systems read and/or write to optical media using a light beam. Traditional optical data storage systems read and/or write to a disk, such as a compact disk (CD). Increasingly, optical data storage systems use optical tape as a storage medium. Optical tape is a long, thin strip of material such as plastic. Optical tape is durable and has large storage capacity compared to optical disks or magnetic tape.
A tape drive may use an optical pickup unit (OPU) comprising an optical head to read and/or write to a tape. A tape may include thousands of parallel tracks that run longitudinally along the length of the tape. To read from a particular track of the tape, an OPU is configured at a lateral position, with respect to the tape, that corresponds to the particular track. A shift in the lateral direction, with respect to the tape, is referred to herein as a movement of the OPU in a tracking direction. Optical heads typically experience shifts in the tracking direction, which can cause tracking errors and subsequent data errors. To compensate for the shift, a system may generate a tracking error signal (TES). The TES is indicative of a lateral position of the OPU with respect to the tape. Based on the TES, the system moves the optical head in a lateral direction to a desired lateral position with respect to the tape. A tracking error signal is commonly normalized, and is referred to as a normalized tracking error signal (NTES). When a tape drive is in operation, the optical head moves to follow or seek tracks. As the optical head moves, the lateral displacement of the optical head relative to other optical components may cause an electrical offset (e.g., an error) in the TES.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.